Ink jet recorders have been the subject of an intense development effort for a number of years. The recorders fall generally into two categories, namely drop-on-demand and continuous stream types. The present invention is directed to the latter type of recorder whose operation is described in detail in U.S. Pat. No. 3,416,153. In general, a continuous ink jet recorder produces a liquid jet by pumping the ink under high pressure through a capillary nozzle unit and directing the jet along a path toward a recording medium such as a paper sheet. As the jet issues from the nozzle it is selectively charged. A transverse electric field deflects the charged portions of the ink jet from the path into a gutter so that they are prevented from reaching the recording medium. The uncharged, and thus undeflected, portions of the jet reach the recording medium and form the printing thereon.
In continuous jet printers, the voltage of the deflection field is quite high. Particles from the ink stream which rebound upon impact with the recording surface instead of adhering to that surface, as well as particles from the ink stream which were deflected, cause an ink mist to develop in the region of the field. The ink mist particles of the different color inks are entrained in the segments of the ink streams that reach the recording surfaces and thus contaminate the color printing on that surface giving it a pronounced background coloration. This ink mist also reduces the voltage of the deflection field and sometimes causes arcing in the field region resulting in improper deflection of the ink streams and irregular printing on the recording surface.
In addition, prior printers of this type are plagued by clogging of their nozzle units by the recording liquid while the ink jet recorder is in operation. This gives rise to increased down-time and increased nozzle relacement costs. Further, none of the prior recorders of which we are aware have permitted simple adjustments by the user of the directions of the ink streams. Nor do they have low cost nozzle and deflection units which are easily removed and positioned.